I am using an Arduino Uno and have used up all it's pins so I have plugged up a Nano to a couple of the Uno's pins and using the Uno's 5v and ground to power the Nano. Is this ok?

It's been working fine until recently. My Uno will no longer allow me to upload code but everything still powers fine and runs on the existing code I had uploaded before. The reset button on the Uno does not work so I assume it's bricked, but it does still operate fine on the code it has, as I said.

Anyway, my question, is it ok to run the Nano like this? Is it using too much of the Uno's current... because the Nano's pins are also all being used. I'm no good at regulating current and just want to make sure that the Nano isn't eating up a bunch of current from the Uno by lighting it's LED's and it's other operations.

  • Are your Arduinos driving heavy loads or are their outputs only connected to high impedance inputs? Commented Jun 24, 2015 at 19:23
  • Nothing too heavy. Uno - motor controller (2 tiny motors), 2 servos, push button. Nano - Several LED's (just a few on at one time) and two range finders. Commented Jun 24, 2015 at 19:33
  • The Nano itself will not draw much current. So, if the sum of your loads is within the Uno's capabilities, it normally should work fine. Commented Jun 24, 2015 at 19:52
  • Two servos is a really heavy load.
    – Wirewrap
    Commented Jan 14, 2016 at 17:18

3 Answers 3


try to connect uno and nano with I2C or serial, with I2C it connected to SCA/SDL pin (analog 4/5) or with serial it connected to tx rx. Make sure you use a pull up resistor. From the main site of arduino there's a tutorial in there but forgot to set up a pull up resistor.


Be careful not to power any sort of motor directly from an Arduino (or any of it's siblings directly) without a transistor or H-bridge in between, unless you know exactly how much current your motor draws, peak, and how much your arduino can supply on any given pin. The same applies to any other high-draw device too.

If you are using LEDs, make sure you have a resistor in series with the LED - google "LED resistor calculator" to help you figure out which resistor you need.

Also, when you upload the program, it uses two of the pins - rx and tx, should be digital pins 0 & 1 on a Uno (any other, check your docs).

  • What are you talking about? I didn't ask any of this. I already know all of this. Terrible response. Commented Jun 24, 2015 at 22:12

Maybe it is a very good idea to connect Arduino UNO's only one DIGITAL out point among other digital output pins. This pin can trig Arduino Nano's analog input pins so that you can work your task for further you needed. But you have to seperate your shields or your motors or other things. Like this:

enter image description here

By the way, if you get an upload error, please plug out your shileds or motors or LEDs then try to upload your code again into Arduino UNO.

  • Connect the GNDs as well.
    – Jot
    Commented Jul 17, 2017 at 12:35

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